1 kg of water, at 20 ° C is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of 20 Ω . The rms voltage in the mains is 200 V . Ignoring heat loss from the kettle, time taken for water to evaporate fully is close to [ Specific heat of water = 4200 J kg - 1 ° C - 1 Latent heat of water = 2260 k J k g - 1 ]

Question

1 kg of water, at 20 ° C is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of 20 Ω . The rms voltage in the mains is 200 V . Ignoring heat loss from the kettle, time taken for water to evaporate fully is close to [ Specific heat of water = 4200 J kg - 1 ° C - 1 Latent heat of water = 2260 k J k g - 1 ], 3 min, 16 min, 22 min, 10 min

MARKS App · Accepted Answer

Given specific heat of the water 4200 J kg - 1 ° C - 1 Latent heat of the water = 2260 k J k g - 1 Q = P × t Q = m c Δ T + m L ⇒ P × t = m c Δ T + m L ⇒ V r m s 2 R × t = m c Δ T + m L ⇒ 200 2 20 × t = 4200 × 80 + 2260 × 10 3 ⇒ t = 1298 s ≃ 22 m i n

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